The considerations which led to the development of the invention started out from a toothed tool for the precision working of gears, the working surfaces of which consist of a mineral material. During a rolling of such a tool on the teeth of the workpiece, due to the different relative sliding relationships over the whole tooth height, different material amounts are removed, so that tooth form or profile errors cannot, in every case, be corrected (German OS No. 23 06 780).
The apparatus of the invention avoids this deficiency by providing a guide-gear pair, which supports the tool or the workpiece. It is true that a guide-gear pair is already known for supporting of the tool during gear shaving, however, same serves an entirely different purpose. That is, gear shaving is done backlash-free. By changing the tooth flanks which are in engagement, a different number of tooth flanks always participate in the shaving operation, which causes different tooth-system errors than the above-described ones. This deficiency was overcome by the said guide-gear pair, which also runs backlash-free. This try was not successful. (German Pat. No. 1 161 465).
The apparatus according to the invention avoids both errors, by the workpiece and tool rolling on one another with backlash; however, the apparatus is designed such that the degree of chip removal started out from a premachined or preworked workpiece. Thus, the tooth thickness of the finished gear could depend from the tooth thickness of the premachined workpiece.
The basic purpose of the invention is to make different chip feeds on the premachined workpiece nondamaging, that is to always achieve the same final size or finished dimension in spite of different chip feeds. This is by all means not an obvious thing to accomplish, because the two tooth sides of the workpiece are machined one after the other (not simultaneously like in the case of the backlash-free machining).
The basic purpose of the invention is attained by providing an apparatus capable of changing or adjusting the relative positions between the workpiece/tool pair and the guide-gear pair. This thought is not only valid for externally toothed workpieces but also for internal gears. The difference with respect to the older suggestion is that in the older suggestion, the depth of the chip removal on the two workpiece tooth flanks started out from the premachined flanks whereas the invention starts out from the just machined flank or one tooth side. The machining of the other tooth side is referenced thereto. Thus the starting dimension for the second flank is the machined first flank.
The invention can also be applied to apparatus in which more than one tool engages the workpiece.
It is particularly important for the machining task according to the invention, that the tooth flank of the workpiece, which is just being machined, is supported by the mating flank on the guide-gear pair.
Also advantageous for the invention is the adjustment of the chip feed, because same is carried out by means of a radial adjustment. The adjustability in peripheral direction is alone reserved for the precision adjustment according to the invention. Of course, this is valid only for the adjustabilities which are started from outside. The actual chip removal occurs in reality in two coordinates, namely, radially through the chip feed by a carriage or the like and in the peripheral direction through the tooth flanks of the guide-gear pair due to the pressure angle at the pitch point.
Further characteristics and advantages of the invention can be taken from the following description.